gazelle-syslog might not handle Syslog UTF-8 messages

Currently, SyslogDecoder decode byte message into a String using system default encoding, which is a bad java practice. At least US-ASCII decoding should be used.

However it might not be sufficient: According to RFC5424, the header must always be encoded in US-ASCII but the message could be either encoded in US-ASCII or UTF-8. So decoding the whole syslog frame without knowing the message format is a mistake.

The current implementation must be rework because it cannot solve the probleme easily: the current RFC5424 parser (who is responsible to parse the header content) take a String as argument, so the frame must have been previously decoded... And it is not possible to know how to decode before having parsed the header...